Whilst the business for RFID (Radio Frequency Identification) tags is starting to take off, manufacturing of these RFID tags is still a compromise. On the one hand, potentially lower cost technologies such as polymer TFTs (Thin Film Transistors) cannot always reach the frequency performance required for the RFID tags (either 13.5 MHz, or the 700-2500 MHz range). On the other hand, whilst the electronics components of the tag (in the order of a few hundred bits of memory and hundred transistors) can be cost effectively manufactured in CMOS, the overall costs of such CMOS based tags are nevertheless high due to the costs for manufacturing the antenna, interconnecting the antenna with the electronics components and packaging the same.
One option to produce RFID tags at a lower cost is to move to LTPS (Low Temperature Poly-Silicon) technology. As LTPS can handle the frequency requirements for RFID tags and is significantly less expensive than CMOS (around a factor of 10), it may be cost effective to integrate both the electronics and the antenna onto a single substrate. However, it turns out that an LTPS based tag system with an area, which is cost effective compared to the known solution, is not sufficiently sensitive for most practical applications. Specifically, a larger antenna would be required—but as this will requires a larger substrate the price of the tag (which in an integrated approach such as LTPS is a linear function of the device area) will increase unacceptably.